1. Field of the Invention
The present invention is directed to the use of an insoluble sulphur as a vulcanizing agent for rubber. In particular, insoluble sulphur is used as a vulcanizing agent for rubber products requiring an adhering step, transparent rubbers prone to scorching, colored rubber products, and the like.
2. Discussion of Background and Material Information
The term "insoluble sulphur" used herein refers to polymerized sulphur which is insoluble in carbon disulfide. Although conventional insoluble sulphur normally contains approximately 10% of soluble sulphur, it is referred herein simply as insoluble sulphur.
Due to its polymerized structure, the insoluble sulphur should be dispersed uniformly in rubber when insoluble sulphur is used.
Conventionally, insoluble sulphur is used in a form of fine grain which is atomized and tends to become lost as dust during use. Further, since the fine grain is likely to be charged or electrified due to friction between grains, it might cause a powder dust explosion. Thus, the use of fine grain sulphur causes problems concerning processing, pollution and be like. Moreover, since the insoluble sulphur is not particularly fluid, it does not exhibit good processing, handling, shipping and storage characteristics.
In order to prevent insoluble sulphur from being dusted, and from being charged, it has been proposed to add rubber processing oil to the sulphur. The proposed idea, however, is unsatisfactory because the insoluble sulphur does not disperse well into rubber. In an attempt to improve the physical property of the sulphur, in particular its dispersing ability into rubber, various other proposals have been made none of which, however, have met with much success.
For example, the Japanese Unexamined Patent Publication No. 49-93294 is directed to granules obtained by addition of oil consisting of processing oil and surfactant to insoluble sulphur with a view to improve the dispersion of the sulphur into rubber. U.S. Pat. No. 3,706,708 discloses adding ethylene glycol ether, a non-ionic activator, to insoluble sulphur so as to accelerate the sulphur dispersion. Both of the proposals succeeded somewhat in improving the sulphur dispersion into rubber but they are still unsatisfactory in that the use of the activator is expensive and because the sulphur itself does not disperse to its full extent.